Inhibitor



252. COMPOSITIONS,

'ratented Nov. 17, 1931 UNITED STATES Exam!" r PATENT OFFICE JOSEPH M. LEAPER, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO E. F. BOUGH- TON AND COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION 01 PENNSYLVANIA INHIBITOR No Drawing.

My invention relates to a new inhibitor and to the process of pickling iron and steel, and more particularly it relates to a new pickling solution which effectively remove scale and rust from the iron and steel without appreciably attacking the surface thereof.

The principal object of my invention is to provide a solution of sulphuric acid or other pickling material in which the pitting and corrosive action of the acid on the iron and steel surface will be reduced to a minimum, and for all practical purposes will be precluded.

A further object of my invention is to provide a solution of sulphuric acid which will be relatively inert toward ferrous metals and which, therefore, can be shipped in the standard iron or steel containers with assurance that the corrosion of the containers will be minimized, or prevented.

Still another object is to provide a process of pickling and a pickling bath which effectively and efficiently removes the scale and rust from the iron and steel without attacking the surface thereof. Other objects will appear from a consideration of the specification and claims.

In the so-called pickling processes sulphuric acid or other scale attacking compounds are used to remove the rust or scale from the surface of iron or steel. Great difficulty is encountered since the acid after removing the scale and rust pits and corrodes the metal below, which action is accompanied by the evolution of disagreeable gases.

It is not possible in commercial practice to remove the scale or rust without also attacking the metal, for there is no means of determining when the scale or rust has been removed. Furthermore, the rust and scale usually do not cover the metal surface uniformly, and, therefore, the acid while dissolving the scale at one point on the surface, attacks the metal itself at some adjacent point where the scale does not exist or has been removed. It is necessary that the surface of the iron and steel remain bright and smooth after treatment with the pickling solution, for otherwise the treated objects are unfit for galvanizing and other uses in the trade.

Application filed August 1, 1930. Serial No. 472,481.

Great difliculties are also encountered in shipping of sulphuric acid, due to the chemical reaction which takes place between the acid and the containers, which are usually made of iron or steel. The life of these containers is,therefore, relatively short and there is always present the hazard of leakage with its attending danger to property and life.

My invention is characterized by the addition of a new compound to the sulphuric acid or other pickling material, which compound minimizes or prevents the acid from attacking the iron or steel surface. The effectiveness of the acid in removing the scale and rust is not reduced and, therefore, a pickling solution with marked advantages is available. Various compounds have previously been suggested for use, but the compounds of the present invention have many advantages over those heretofore known. The class of compounds of the present invention are effective, easy to handle, and stable in the pickling bath.

My invention contemplates the addition of an or anic thiosglphate to the pickling bath. e addition of compounds of this class in relatively small amounts for all practical purposes prevents any pitting or corrosive action of the sulphuric acid on the iron and steelv tha .term ifo ganiathi sulphate I includ e the-compounds of the genera formula R.S.SO .OM, where R is an organic radical and where M is'a me al. It W1 e seen at in the formula for thiosulphuric acid (HS;SO Q,OH) the hydrogen of the SH group has been replaced by an organic radical, while the hydrogen of the OH group has been replaced by a metal. The or 'anic radical m be any one of a wide variety of groups, but it 1s preferably a carbon-hydrogen radical, such as anglkyl, an

alkylene, or an aryl group. For example, the

metals are the most satisfactory.

The organic thiosulphates need not be chemically. pure, and may contain other compounds which may or may not also be inhibitors. The organic thiosulphate may be used in a crude form and need not be purified before use. The compound may be prepared in any desired manner, and the following method of preparation of sodium; b er 1 zyl thiosulpbate is given as one optional method and as illustrative.

In an example, 3600 grams of sodium thiosulphate crystals are dissolved in 3600 cc. of water, and to this mixture is added 1660 cc. of benzyl chloride and 432 cc. of denatured alcohol. The mixture is agitated thoroughly and heated gradually to a temperature of 80 degrees centigrade. After a period of one hour at this temperature, 644 grams of common salt are added and the mixture allowed to cool. The crude sodium benzyl thiosulphate crystallizes out, is filtered, pressed and dried at room temperature.

In making up a pickling bath, one-half pound of the sodium benzyl thiosulphate may be added to 1,000 pounds of 20% sulphuric acid. This pickling bath may be used effectively at about 160 degrees F. in the pickling of iron and steel. The oxide and scale are removed with only a very slight action on the metal surface.

The percentage of the organic thiosulphate to be added to the sulphuric acid varies considerably, depending on the nature of the material being treated and the amount of scale or rust to be removed. In general, the amount added will be between 1 pound of compound to 3,000 pounds of dilute acid and 1 pound of compound to 1,000 pounds of dilute acid. The use of higher percentages of compound does not deleteriously effect the pickling action, but usually represents a loss of the thiosulphate. While in the specific example sodium benzyl thiosulphate is mentioned, corresponding proportions of the other organic thiosulphates, such as the alkyl thiosulphates, for example sodium ethyl thiosulphate, or other aryl thiosulphates, may be used in place thereof. Sulp huric acid issps maen di h other pickling {itfiillizllsetl in its E3 1;.iiiillii lilibliili fiieiiiacidsor.the.Mid sulphate salts, The term sulphuric acid 5 sensed in the specification and claims is intended to cover such other pickling compounds.

Other compounds may be used in combination with the organic thiosulphate and they may be inhibitors themselves, or added for other reasons, for instance, for the purpose of inc easing the foam. The addition of crud n I 1 11 cer an instances increases tie efiiciency of the bath. The amount of pyridine to be added depends on the circumstances under which the bath is to be used, but in general may be used in proportions equal to the organic thiosulphate added.

Considerable modification is possible in the choice of the organic thiosulphates and in the percentages used with the pickling compounds without departing from the essential features of the invention.

I claim:

l. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of an organic thiosulphate.

2. The process of pickling iron and steel objects which comprises subjecting said objects to the act-ion of a relatively weak sulphuric acid solution to which has been added a small quantity of a thiosulphate in which the hydrogen of the SH group has been replaced by a carbon-hydrogen organic radical.

3. The process of ickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of an aryl substituted thiosulphate.

4. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a smal quantity of an aryl substituted thiosulphate.

5. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of an alkali alkyl substituted thiosulphate.

6. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of an alkali aryl substituted thiosulphate.

7 The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added ahsmall quantity of sodium ethyl thiosulp ate.

8. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of sodium benzyl thiosulphate.

9. A pickling bath for removing scale and rust from iron and steel comprising a. relatively weak sulphuric acid solution and a small quantity of an or anic thiosulphate.

10. A pickling bath or removing scale and rust from iron and steel comprising a relatively weak sulphuric acid solution to which has been added a small quantity of 9.

252. COMPOSITIONS, V

thiosulphate in which the hydrogen of the SH group has been replaced by a carbonhydrogen organic radical.

11. A pickling bath for removing scale and rust from iron and steel com using a relatively weak sulphuric acid so ution to which has been added a small quantity of an alkyl substituted thiosulphate.

12. A pickling bath for removing scale and rust from iron and steel comprising a relatively weak sulphuric acid solution to which has been added a small quantity of an aryl substituted thiosulphate.

13. A pickling bath for removing scale and rust from iron and steel comprlsing a. relatively weak sulphuric acid solution to which has been added a small uantity of an alkali alkyl substituted thiosu phate.

14. A pickling bath for removing scale and rust from iron and steel comprising a.

relatively weak sulphuric acid solution to which has been added a small quantity of an alkali aryl substituted thiosulphate.

15. A pickling bath for removing scale and rust from iron and steel comprising a relatively weak sulphuric acid solution to which has been added a small quantity of sodium ethyl thiosulphate.

16. A pickling bath for removing scale and rust from iron and steel comprising a relatively weak sulphuric acid solution to which has been added a small quantity of sodium benzyl thiosulphate.

17. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a small quantity of an organic thiosulphate and pyridine.

18. The process of pickling iron and steel objects which comprises subJecting said objects to the action of a relatively weak sulphuric acid solution to which has been added a. small quantity of sodium benzyl thiosulphate and pyridine.

-.- and a small quantity of pyridine.

JOSEPH M. LEAPER.

Exa 

